Download Chapter 11 Force and Newton`s Laws Laws

Chapter 11
Force and Newton’s
Laws
Section 1 – Pages 310 - 315
Newton’s 1st Law
Mass and Inertia
The mass of an object affects how easy it
is to change its motion.
motion.
– Recall that mass is the amount of matter in an
object.
– The tendency of an object to resist a change
inertia..
in motion is called inertia
– The inertia of an object increases as the
increases..
object’s mass increases
Momentum
Just as increasing the mass of an object makes it
harder to stop, so does increasing the speed or
velocity of an object.
The momentum of an object is a measure of how
hard it is to stop the object, and it depends on the
object’s mass and velocity.
The symbol for momentum is p.
The units for momentum are kg ● m/s in the
direction of the velocity.
velocity.
Momentum (Practice Problems)
A 10,000 kg train is traveling east at 15 m/s.
Calculate the momentum of the train.
p=m*v
p = 10,000 kg * 15 m/s East
p = 150,000 kg · m/s East
What is the momentum of a car with a mass of
900 kg traveling north at 27 m/s?
p=m*v
p = 900 kg * 27 m/s North
p = 24,300 kg · m/s North
Law of Conservation of
Momentum
In any collision, momentum is transferred from
one object to another.
Example – Cue ball hits other billiard balls.
The Law of Conservation of Momentum states that
the total momentum of a group of objects remains
constant unless outside forces act on the group.
FORCES
The Nature of Force:
– A force is a PUSH or a PULL that gives energy
to an object.
– EXAMPLES OF FORCES:
Combining Forces
The combination of all the forces acting on
an object is the net force.
force.
When these forces are unbalanced
unbalanced,, this
causes an object to start moving, stop
moving or change direction.
direction.
Unbalanced forces acting on an object will
change the object’s motion.
Combining Forces
Unbalanced Forces (change motion)
– Two forces acting in the same direction
combine by adding together.
EX - dogs pulling a sled team
Combining Forces
Unbalanced Forces (change motion)
– Two forces acting in opposite direction
combine by subtraction
subtraction..
– If one force is greater than the other force,
the overall force is in the direction
of the greater force
Ex. – Pushing open a door.
Combining Forces
Balanced Forces (no change in
motion)
– Equal forces acting on one
object in opposite directions are
called balanced forces.
forces.
– Balanced forces acting on an
object will NOT change
the objects motion.
Example – Pushing on
a wall.
Explain the Example
Unbalanced Forces in opposite direction (Push)
Explain the Example
Balanced Forces in opposite directions (Pull)
Explain the Example
Tailwind
Unbalanced Forces in same direction (Push)
Balanced vs. Unbalanced Forces
Newton’s 1st Law of Motion
Newton’s 1st Law of Motion states:
An object at rest will continue to stay at
rest AND an object in motion will continue
to stay in motion unless acted on by an
outside force.
Therefore, since inertia is the tendency of
an object to resist motion…..
motion…..
Newton’s 1st Law of Motion is also known
as the Law of Inertia.
Newton’s 1st Law of Motion
Remember, the amount of inertia an
object has depends on its mass
mass..
The greater the mass of an object the
greater the inertia.
Which is easier to move?
Which has more inertia?
FRICTION
The force that opposes motion is known as
friction.
Friction is a force that acts to oppose sliding
between two surfaces that are touching.
FRICTION Creates……
Rubbing your hands together
creates friction TRY IT! What
Happens?
Friction creates heat!
Apply more pressure to your
hands, what does it do?
Pressure increases the amount of
friction!
Now try rubbing only ONE FINGER
along your palm? What happens
to friction?
A smaller surface area decreases
friction!
Factors that affect friction
Surface Area – As surface area increases
between surfaces, so does friction
(more rubbing = more friction).
Texture – A rougher surface = greater friction.
A smoother surface = less friction.
Mass/Weight – The greater the mass or weight
of an object, the more friction it will create.
Fluids – Fluids reduce friction by preventing
surfaces from coming into contact.
Galileo’s Ideas About Motion
It is the force of friction that usually
makes moving objects slow down
and come to a stop.
To keep objects moving, a force has
to be applied to overcome the force
of friction.
If friction could be removed, an
object in motion would continue to
move with a constant velocity.
Different types of Friction
There are a few different
types of Friction:
– 1. Static Friction
– 2. Sliding Friction
– 3. Rolling Friction
– 4. Fluid Friction
STATIC FRICTION
#1 STATIC FRICTION:
– Have you ever tried to push something HEAVY?
– The type of friction that prevents a stationary object
from moving when a force is applied is static friction.
(The object is still and you are trying to move it!)
The rougher the surface, the larger the surface area, or the
greater the mass = MORE STATIC friction
Sliding and Rolling Friction
#2 Sliding Friction
– When solid surfaces slide over one another
Example: Match striking a surface
#3 Rolling Friction
– When an object rolls over a surface (less force
needed than sliding friction – WHY?)
Example: Bicycle tire on sidewalk
Fluid Friction
#4 Fluid Friction
– When an object moves through a liquid or a
gas, the fluid reduces friction by preventing
objects from coming into contact.
Why can Friction be useful?
Slows things down!
Without friction you could not
– Walk around
Or
– Move around
Or
– Drive a car
Imagine playing basketball in your socks or
walking with sneakers on ice!
How can we reduce friction?
THE END